This invention relates to fluoropolymer compositions having imidate groups, to the curing therefrom and articles containing the at least partially cured compositions.
Fluorine-containing polymers (also known as xe2x80x9cfluoropolymersxe2x80x9d) are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers, uncrosslinked fluoroelastomer gums, and semi-crystalline fluoroplastics. Fluoroelastomers exhibit significant tolerance to high temperatures and to harsh chemical environments. Consequently, they are particularly well adapted for use as seals, gaskets, and other molded parts in systems that are exposed to elevated temperatures and/or harsh chemicals. Such parts are widely used in the chemical processing, semiconductor, aerospace, and petroleum industries, among others.
Fluoroelastomers often include a cure-site component to facilitate cure in the presence of a catalysts. One class of useful cure-site components includes nitrite group-containing monomers, which, in the presence of catalysts, form triazines. These cure-catalysts are typically organotin catalysts, ammonium salts, or ammonia-generating compounds. Such catalysts, however, may be toxic, and/or may release considerable amounts of ions such as undesirable extractable metal residues in the cured materials.
In one aspect, the invention relates to a composition that a fluoropolymer having pendant imidate groups, which imidate groups have the formula: xe2x80x94Cxe2x95x90NH(OR) wherein R is a C1-C10 (preferably C1-C5) aliphatic group which aliphatic group may have F or Cl substituents. The imidate groups can be attached directly to the polymer backbone, e.g., F2Cxe2x95x90CFxe2x80x94Cxe2x95x90NH(OR) or can be part of a longer side chain, e.g., F2Cxe2x95x90CFxe2x80x94(CF2)mxe2x80x94(ORf1)nxe2x80x94(ORf2)pxe2x80x94(CF2)qxe2x80x94Cxe2x95x90NH(OR), wherein Rf1 is a perfluoroalkyl of 1 to 8, preferably 1 to 3, carbon atoms, Rf2 is Rf1 or a perfluoroalkoxy of 1 to 15, preferably 1 to 8, carbon atoms, and R is selected from an aliphatic group having from 1 to 10, preferably 1 to 5, carbon atoms which aliphatic group may have F or Cl substituents, m, n, p, and q are, independently, 0-10, and the imidate group can be terminal or at any other position along this longer side chain. The amounts of the imidate containing structure is from 0.01-5 mol %, preferably 0.2-3 mol %.
The fluoropolymer composition can further include perfluorovinyl ethers of the general formula
CF2xe2x95x90CFO(Rxe2x80x2fO)a(Rxe2x80x3fO)bRf
where Rxe2x80x2f and Rxe2x80x3f are the same or are different linear or branched perfluoroalkylene groups of 1-6 carbon atoms; a and b are, independently, 0 or an integer from 1 to 10; and Rf is a perfluoroalkyl of 1 to 8, more preferably having 1 to 4 (most preferably 1) carbon atom(s), or a perfluoroalkoxy of 1 to 15, more preferably 1 to 8, carbon atom(s).
The fluoropolymer composition also may include interpolymerized units derived from tetrafluoroethylene (TFE), optionally chlorotrifluoroethylene (CTFE), and one or more ethylenically-unsaturated monomers represented by the formulas CF2xe2x95x90CFxe2x80x94Rf1, CF2xe2x95x90CFxe2x80x94Oxe2x80x94Rf2, and CH2xe2x95x90CR2, wherein Rf1 and Rf2 are as defined above, and wherein each R is independently selected from an aliphatic group having from 1 to 10, preferably 1 to 5, carbon atoms which aliphatic group may have F or Cl substituents.
In other aspects, the invention provides a method of making a fluoropolymer comprising polymerizing a composition comprising (i) a fluoropolymer having a backbone, the fluoropolymer having interpolymerized units derived TFE, optionally CTFE, and one or more ethylenically-unsaturated monomers represented by the formulas CF2xe2x95x90CFxe2x80x94Rf1, CF2xe2x95x90CFxe2x80x94Oxe2x80x94Rf2, and CH2xe2x95x90CR2 wherein Rf1 is a C1-C8perfluoroalkyl, Rf2 is Rf1 or a C1-C15 perfluoroalkoxy, and each R is independently selected from H, F, Cl, or a C1-C8 aliphatic group which aliphatic group may have F or Cl substituents; and (ii) imidate groups pendant from the fluoropolymer backbone, which imidate groups have the formula: xe2x80x94Cxe2x95x90NH(OR) wherein R is a C1-C10 aliphatic group which aliphatic group may have F or Cl substituents; and optionally, (iii) a perfluorovinyl ether of the general formula:
CF2xe2x95x90CFO(Rxe2x80x2fO)a(Rxe2x80x3fO)bRf2
wherein Rxe2x80x2f and Rxe2x80x3f are the same or are different C1-C6 linear or branched perfluoroalkylene groups; a and b are, independently, 0 or an integer from 1 to 10; and Rf2 is a C1-C8 perfluoroalkyl group or a C1-C15 perfluoroalkoxy group. This composition further can be shaped, cured, and optional heat aged.
The invention also provides fluoropolymer articles comprising the curable or cured compositions described.
The composition retains the advantages of fluoropolymers having nitrogen-containing cure site monomers such as the high temperature performance properties and chemical resistance typically achieved when organotin compounds are used as the catalyst system with such cure site monomers.
The inventive fluoropolymer system is substantially ion-free. In addition, low molecular weight cure promoters, e.g., perfluoro imidates or nitrites, can be incorporated into the inventive fluoropolymer system to adjust the processing parameters and/or end use properties.
The compositions are useful in applications where polymer stability (e.g., thermal stability) and/or chemical resistance are important. They are also useful in silicon wafer fabrication applications.
The details of presently preferred embodiments of the invention are set forth in the accompanying description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims.